From Prospect to Producing Well: Where Drilling Fits
The stages of a well from exploration idea to abandonment, and the decisions drilling supports at each stage.
11 min
Activities: 0 of 2
A well is a long project, not a short job
Drilling is the most visible part of an oil or gas project, but it sits inside a longer chain. Geologists and geophysicists find a prospect. Engineers plan a well to test it. The rig drills and completes the well. Production engineers operate it for many years. At the end, the well is plugged and abandoned. Decisions made while drilling, such as casing choice or cement quality, affect the well for its whole life.
In this course, a well means the hole, the casing and cement that line it, and the equipment at the top (the wellhead). The drilling phase runs from moving the rig onto the location to handing the well over for completion or production.
The life of a well
- 1
Explore
Prospect and decision to drill
Seismic data and regional geology suggest a trap. The company decides whether the chance of success justifies the cost of a well. - 2
Plan
Well design
Engineers predict pressures, choose casing points, mud and cement, and write the drilling programme and risk register. - 3
Drill
Construction
The rig drills each hole section, runs casing, cements it, and tests the barriers before drilling ahead. - 4
Evaluate
Logging and testing
Logs, cores and tests show whether the reservoir holds oil or gas in useful amounts. - 5
Complete
Completion
Production tubing, packers and the production tree are installed, and the reservoir is connected to the well. - 6
Produce
Operation
The well produces for years. Annulus pressures and integrity are monitored. - 7
Abandon
Plug and abandonment
Cement plugs restore the natural seals so that fluids cannot move between formations or to surface, permanently.
Types of well
Worked example 1: an exploration well
An exploration well targets a sandstone at about 3,200 metres. No well has been drilled within 20 kilometres. The planning team has only seismic data to predict pore pressure. They plan an extra casing string as a contingency, in case pressure rises faster than expected. During drilling, the mud logger sees rising gas readings and a change in cuttings at 2,700 metres. The team uses the contingency string, which the plan had already allowed for.
Worked example 2: a development campaign
A company drills twelve wells from one onshore pad. The first well takes 28 days. The team records every delay and holds a short review after each well. By well six, the time has fallen to 19 days, mainly from better hole cleaning practice and fewer equipment waits. Development drilling rewards careful learning more than exploration does.
Match the well type to its purpose
- Exploration well
- Appraisal well
- Development well
- Injection well
Why does an exploration well usually include a contingency casing string in its plan?